The Effect of the Particle Gradation and Pre-Treatment of Aggregate on the Performance of Alkali-Activated Slag Non-Sintered Lightweight Aggregate Concrete

Non-sintered lightweight aggregate (NSLA) produced by pelletizing and autoclaved curing has received widespread attention due to its environmental protection. However, the effect law of its characteristics, such as particle gradation and water absorption, on the performance of concrete still lacks clear understanding. In this study, seven different gradation types of concrete were designed to investigate the influence of the particle gradation (particularly particle size) of NSLA on the mechanical properties, especially the axial compressive performance, of alkali-activated slag non-sintered lightweight aggregate concrete (AN-LAC). Meanwhile, the different pre-treatment methods for NSLA were also studied to reduce the drying shrinkage of AN-LAC caused by the high water absorption of NSLA. The results showed that the compressive strength, splitting tensile strength, and flexural strength of AN-LAC at 3 d, 7 d, and 28 d showed an increasing trend when the average particle size decreased. The compressive strength of AN-LAC containing 3~5 and 6~10 mm NSLA at 28 days reached the maximum value of 56.7 MPa. AN-LAC containing NSLA with a small particle size exhibited improved elastic modulus. And the modified elastic modulus prediction model of AN-LAC was established considering the effect of particle size of NSLA. The NSLA, which was modified by using a silicone hydrophobic agent and pre-wetted by soaking in water, respectively, could enhance the strength of AN-LAC at 28 days. Combined with the analysis of the microscopic morphology of the ITZ, the shrinkage rate of the concrete with pre-wetted NSLA and modified NSLA at 90 days decreased by 17.7% and 10.3%, respectively.